Single wafer backside wet clean

ABSTRACT

A method and apparatus for cleaning a backside of a substrate is disclosed. The method includes placing the substrate parallel to a platter, wherein the backside of the substrate is facing a top side of the platter in a spaced apart relation, thus defining a gap therebetween. Subsequently, a liquid is flowed through the platter and into continuous contact with the entire backside of the substrate and the top side of the platter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 09/891,849, filed on Jun. 25, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/603,792, filed on Jun. 26, 2000, both of which are hereby incorporated by reference in their entireties. Priority to both U.S. patent application Ser. Nos. 09/891,849 and 09/603,792 are claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of cleaning of a substrate surface and more particularly to the backside cleaning of a single semiconductor wafer.

2. Background of the Related Art

In semiconductor substrate (wafer, substrate or other workpeice) cleaning, particle removal is essential. Generally, most particle removal processes focus on the device side of a wafer as contamination left on the device side can cause a malfunctioning device. However, removing backside particles from a wafer is just as important. Contamination left on the non-device side (backside) can also cause a number of problems. Backside contamination can cause the photolithography step on the front side to be out of focus. Contamination on the backside can cause contamination of the processing tools, which in turn can contaminate the front side of the wafer. Additionally, metallic contamination on the backside, when present during a high temperature operation, can diffuse through the silicon wafer and contaminate the device side of the wafer and cause device defects.

Particles can be removed by chemical means or by mechanical means. In current state of the art, particles are usually removed by both a combination of mechanical means and chemical means. The current state of the art is spray processing to clean the non-device side of a wafer. Alternatively, a batch process that places a number of wafers into a bath filled with a liquid may be used. Optionally, high frequency (megasonic) irradiation may be applied to the liquid to enhance the cleaning process.

In addition, some semiconductor device fabrications utilize hydrophobic wafers. Hydrophobic wafers tend to repel liquids. Consequently, backside cleaning of hydrophobic wafers with conventional methods of cleaning has not been effective or efficient. Currently, there are no effective single wafer cleaning techniques that are able to sufficiently clean both sides of a hydrophobic wafer simultaneously.

Therefore, there remains a need for a more effective and efficient process suitable for a single wafer back-side cleaning.

SUMMARY OF THE INVENTION

Methods are disclosed for cleaning a backside of a substrate in a single substrate cleaning tool. In one embodiment, a method is provided for cleaning a backside of a substrate that includes placing the substrate parallel to a platter, wherein the backside of the substrate is facing the top side of the platter in a spaced apart relation, thus defining a gap therebetween and flowing a liquid through the platter and into continuous contact with the entire backside of the substrate and the top side of the platter.

In another embodiment, a method is provided for cleaning a backside of a substrate that includes placing the substrate parallel to a platter having a top side and a bottom side, wherein the backside of the substrate is spaced apart from the top side of the platter forming a gap between the backside of the substrate and the top side of the platter and filling the gap with a cleaning liquid provided through the platter.

In another embodiment, a method is provided for cleaning a backside of a substrate that includes placing the substrate parallel to a platter having a top side and a bottom side, wherein the backside of the substrate is facing the top side of the platter in a horizontal orientation. Then the backside of the substrate is spaced approximately 3.0 to 4.0 millimeters from the top side of the platter. Subsequently, a cleaning liquid is flowed through the platter into continuous contact with the entire backside of the substrate and the top side of the platter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited aspects of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 is a sectional view of one embodiment of a wafer cleaning chamber;

FIG. 2 is a partial sectional view of one embodiment of a center-section of a platter and a wafer having a flow of liquids therebetween;

FIG. 3 is a top plan view of one embodiment of a wafer holding bracket;

FIG. 4 is a perspective view of the platter having a wafer disposed on a bracket; and

FIG. 5 is a flow diagram of one embodiment of a sequence for cleaning the backside of a wafer.

To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Aspects of the invention will be described below in reference to a process chamber that can process either or both a top and bottom side of a single substrate or wafer in chip processing. It is to be noted, that hereinafter substrate and wafer may be used interchangeably. A suitable process chamber includes the process chamber disclosed in U.S. application Ser. No. 09/891,849, filed on Jun. 25, 2001, which is incorporated by reference. Additional suitable process chambers include the TEMPEST™ family of chambers available from Applied Materials, Inc., of Santa Clara, Calif. It is contemplated that other systems, including those available from other manufacturers may be utilized.

FIG. 1 is a sectional view of one embodiment of a single wafer cleaning chamber 100. The chamber 100 is configured to expose a non-device side 114 of a wafer 106 to cleaning, rinsing and drying chemicals. In one embodiment, the non-device side 114 of the wafer 106 is facing towards a through hole (feed port) 142 for exposure to cleaning chemicals provided from a chemical source 112, while a device side 116 of the wafer 106 is facing away from feed port 142.

In one embodiment, to initiate a wafer process cycle, a platter 108 translates along an axis 145 a distance downward and a rotatable wafer holding bracket (bracket) 148 moves to a position to receive the wafer 106. A robot arm (not shown) holding the wafer 106 enters the interior of a chamber body 160 of the chamber 100 through an access door 158 and the wafer 106 is placed on the bracket 148. The platter 108 is then raised so as to position the wafer 106 in a spaced apart relation above the platter 108. Although in the present exemplary embodiment platter 108 is circular, those skilled in the art will recognize that the geometry of platter 108 may be any geometry substantially similar in size to substrate 106.

In one embodiment, the wafer 106, resting in the bracket 148 in the process position, is parallel to the platter 108 and spaced a distance from the platter 108, thereby creating a gap 102. The platter 108 is flat where it faces the wafer 106 and therefore, the distance separating the platter 108 and the wafer 106 is uniform. The gap 102 between the wafer 106 and the platter 108 is set such that a liquid flowing through the gap 102 may contact both the platter 108 and backside of the substrate 106. In one embodiment, the distance across the gap 102 may be directly correlated to the viscosity of a liquid, such as the cleaning chemicals provided from the chemical source 112, used to clean the non-device side 114 of the wafer 106. The distance across gap 102 may be in the range of approximately 0.5-10.0 millimeters (mm) and preferably between 3.0-4.0 mm.

In one embodiment, the wafer 106 when positioned in the bracket 148 can rest on three or more vertical support posts (posts) 110 of the bracket 148. The posts 110 can contain an elastomer pad (shown in FIG. 3) to contact the wafer 106 directly. The wafer 106 may be rotated while cleaning chemicals are dispensed from below to contact the non-device side 114 of the wafer 106. Cleaning chemicals may be any type of chemicals used to clean wafers in semiconductor chip fabrication, such as for example, isopropyl alcohol, hydrofluoric acid, standard clean-1 solution (hydrogen peroxide, ammonium hydroxide and water), de-ionized water, any combination thereof or any other suitable cleaning fluids.

A tube 128 connects the chemical source 112 to the platter 108. The platter 108 has a feed port 142 through which cleaning chemicals delivered through the tube 128 are provided to the non-device side 114 of the wafer 106. Although only a single hole in feed port 142 is shown in the present embodiment, platter 108 may have a plurality of holes. Moreover, the platter 108 may be made of any porous material, such as for example, a sponge-like material. In addition, platter 108 may be a static plate or a plate with megasonics, as disclosed in U.S. Patent Publication No. 2002/0029788, which is hereby incorporated by reference in its entirety.

In addition, a nozzle 117 may be positioned above the wafer surface over the outer half of the wafer 106. The nozzle 117 can apply a stream of inert gas 113, such as Nitrogen (N₂) or additional cleaning fluids.

Cleaning chemicals placed between the wafer 106 and the platter 108 can be maintained in position by natural forces such as capillary action and surface tension. A volume defined within the gap 102 and bounded at an edge 115 of the wafer 106 is substantially filled by the cleaning chemicals provided between the wafer 106 and the platter 108. Consequently, the cleaning chemicals are in continuous contact with the entire non-device side 114 of the wafer 106 and a top side of the platter 108. Thus, full immersion of the wafer non-device side 114 is simulated.

Furthermore, a chemical flow rate required to maintain the cleaning chemicals against the non-device side 114 can be reduced during processing, resulting in less chemicals used for each process. The reduction in chemicals also allows for economic use of single use chemicals. During the cleaning portion of the process, the wafer rotation may be stopped allowing the wafer 106 to remain still while the cleaning chemicals contact the non-device side 114 of the wafer 106. The wafer 106 can be rotated, however, to wet out the non-device side 114 of the wafer 106 initially with the cleaning chemicals as well as for the rinse and dry cycles. The wafer 106 may also be oscillated or vibrated.

FIG. 2 is an illustration of one embodiment of the center section of the platter 108 and the wafer 106 having a flow of cleaning chemicals therebetween. The platter 108 has a topside 217 and a bottom side 219. The platter topside 217 faces the non-device side 114 of the wafer 106. The platter 108 may be able to translate along rotational axis 145 to increase the distance across the gap 102 during wafer rinse and/or dry cycles. The robot arm (not shown) can place the wafer 106 in the bracket 148 such that the wafer device side 116 is facing up and away from the platter 108. When placed in the bracket 148, the wafer 106 can be centered over, and held substantially parallel to, the platter 108 to create the gap 102. The distance across the gap 102 may be approximately between 3.0-4.0 mm, but may fall within a larger range of approximately 0.5-10.0 mm. Positioned beneath the platter 108 can be an electric motor (not shown) for rotating the bracket 148. A through hole (not shown) can exist in the electric motor through which wiring may be passed from the platter 108 as well as a tube 128 for transferring cleaning chemicals from the chemical source 112 to the feed port 142.

In one exemplary embodiment of the present method, bracket 148 rotates wafer 106 while the cleaning chemicals are applied from below such that the chemicals are in simultaneous and continuous contact with the platter 108 and the entire non-device side 114 of the wafer 106. As depicted by arrows 202, the cleaning chemicals substantially fill the volume created by the gap 102 to the edge 115 of the wafer 106.

During the cleaning, rinse and dry cycles, the wafer 106 may be rotated at a selected revolution per minute (rpm) about an axis 145 that runs through the pivot point of the bracket 148. Additionally, to optimize any particular cycle, the wafer spin rate may be stopped or varied by changing the power setting. In one embodiment, the bracket 148, powered by the motor (not shown), can rotate the wafer 106 during cleaning operations at an rpm of approximately between 0-1000 rpm and during the dry and rinse cycles at an rpm of greater than 250 rpm, wherein a range of approximately between 250-6000 rpm is preferable.

FIG. 3 illustrates a top plan view of one embodiment of the rotatable wafer holding bracket 148. FIG. 4 illustrates a perspective view of the bracket 148 holding the wafer 106. Both views will be discussed simultaneously for the purpose of clarity. The wafer 106 (shown in dashed line) can be held in place by the bracket 148 to position the wafer 106 parallel to and near the platter (not shown for clarity). Initially, the bracket 148 can hold the wafer 106 by gravity at four points 409 and 409′ along the edge 115 such that the device side 116 and the non-device side 114 of wafer 106 are clear of the bracket structure and fully exposed to cleaning/rinsing liquids. The number of contact points 409 and 409′ between the bracket 148 and the wafer 106 may be at least three. The portion of the bracket 148 in contact with the wafer 106 can be made with an elastomeric material such as a plastic or rubber to friction grip the wafer 106 during the start and stop phases of rotation. In one embodiment, the contact points are O-rings that are positioned at the ends of bracket support posts (posts) 411.

FIG. 5 is a flow diagram illustrating one embodiment of a method 500 for cleaning the backside of a substrate. The method 500 is described in conjunction with chamber 100 of FIG. 1, as an example for clarity, but one skilled in the art will recognize that method 500 may be practiced on other systems. The method 500 begins at step 510 by placing the substrate 106 in the chamber 100. Substrate 106, such as a semiconductor wafer, is placed on bracket 148 at a distance from the platter 108. In one embodiment, the substrate 106 is placed horizontally and parallel to the platter 108.

Once the substrate 106 is properly placed in chamber 100, the process proceeds to step 520 where the height of bracket 148 is adjusted such that the substrate 106 may be set at an appropriate distance from platter 108. The distance between the non-device side 114 of substrate 106 and the top side of platter 108 form the gap 102.

As discussed above in an exemplary embodiment, the appropriate distance across the gap 102 may be set in response to the viscosity of the cleaning chemicals. The higher the viscosity of the cleaning chemicals, a larger distance across the gap 102 may be used. Likewise, the lower the viscosity of the cleaning chemicals, a shorter distance across the gap 102 must be used. Using a 300 mm substrate and typical backside wafer cleaning chemicals such as, for example, isopropyl alcohol, standard clean-1 (i.e. hydrogen peroxide, ammonium hydroxide and water), de-ionized water, or any combination thereof, the distance across the gap 102 may be in the range of 0.5-10.0 mm and more preferably in the range of 3.0-4.0 mm.

At step 530, the method 500 proceeds by flowing a liquid, such as cleaning chemicals provided by chemical source 112, through platter 108 to fill gap 102. As discussed above, the distance across the gap 102, measured from the non-device side 114 of substrate 106 to the top side of platter 108, is such that the flow of liquid through platter 108 substantially fills the volume created by gap 102 to the edge 115 of the substrate 106. By filling the volume created by gap 102 to the edge 115 of the substrate 106 with liquid, the liquid is in continuous contact with the entire non-device side 114 of the substrate 106 and the top side of platter 108. As a result, the non-device side 114 of the substrate 106 is cleaned by simulating full immersion of the substrate 106. Such a result is advantageous for certain substrates such as, for example, hydrophobic wafers that tend to repel liquids away from the wafer surface, and because less cleaning fluids are required compared to full immersion techniques.

At step 540, the bracket 148 holding the substrate may be rotated while flowing liquid through platter 108. Rotating bracket 148 helps to achieve more uniform coverage of the liquid on the non-device side 114 of substrate 106.

While the foregoing is directed to the exemplary aspects of the invention, other and further aspects of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A method for cleaning a backside of a substrate, comprising: placing a substrate parallel to a platter, wherein a backside of the substrate is facing a top side of the platter in a spaced apart relation, thus defining a gap therebetween; and flowing a liquid through the platter and into continuous contact with the top side of the platter and the entire backside of the substrate.
 2. The method of claim 1, further comprising: holding the substrate in a bracket above the platter; and rotating the bracket while simultaneously performing the flowing step.
 3. The method of claim 1, wherein the placing step further comprises placing the substrate parallel to the platter in a horizontal orientation.
 4. The method of claim 1, wherein the substrate comprises a hydrophobic semiconductor wafer.
 5. The method of claim 1, wherein the platter comprises a porous material.
 6. The method of claim 1 further comprising setting a distance across the gap in response to a viscosity of the liquid.
 7. The method of claim 1, wherein a distance across the gap defined between the backside of the substrate and the top side of the platter is approximately 3.0 to 4.0 millimeters.
 8. The method of claim 1, wherein the liquid comprises at least one of isopropyl alcohol, hydrogen peroxide, ammonium hydroxide, water or de-ionized water.
 9. A method for cleaning a backside of a substrate, comprising: placing a substrate parallel to a platter having a top side and a bottom side, wherein a backside of the substrate is spaced apart from the top side of the platter, thereby forming a gap between the backside of the substrate and the top side of the platter; and filling the gap with a cleaning liquid provided through the platter.
 10. The method of claim 9, further comprising: rotating the substrate while the cleaning liquid is in the gap.
 11. The method of claim 9, wherein the placing step further comprises placing the substrate in a horizontal orientation above the platter.
 12. The method of claim 9, wherein the substrate comprises a hydrophobic semiconductor wafer.
 13. The method of claim 9, wherein the platter comprises a porous material.
 14. The method of claim 9 further comprising setting a distance across the gap in response to a viscosity of the cleaning liquid.
 15. The method of claim 9, wherein a distance across the gap between the backside of the substrate and the top side of the platter is approximately 3.0 to 4.0 millimeters.
 16. The method of claim 9, wherein the cleaning liquid comprises at least one of isopropyl alcohol, hydrogen peroxide, ammonium hydroxide, water or de-ionized water.
 17. A method for cleaning a backside of a substrate, comprising: placing a substrate parallel to a platter having a top side and a bottom side, wherein the backside of the substrate is facing the top side of the platter in a horizontal orientation; spacing the backside of the substrate approximately 3.0 to 4.0 millimeters from the top side of the platter; and flowing a cleaning liquid through the platter into continuous contact with the entire backside of the substrate and the top side of the platter.
 18. The method of claim 17, further comprising: rotating the substrate while flowing the cleaning liquid into contact with the substrate.
 19. The method of claim 18, further comprising: stopping the flow of cleaning liquid.
 20. The method of claim 19, further comprising: increasing a rotating speed of the substrate after stopping the flow of cleaning liquid.
 21. The method of claim 20, further comprising: increasing the spacing between the substrate and the top side of the platter after stopping the flow of cleaning liquid. 